This invention relates to an engine knock control apparatus.
The engine knock control apparatus detects knocking of an internal combustion engine as a knock signal by means of a knock sensor and controls a spark timing by the detected knock signal.
The engine knock control apparatus of this kind is disclosed in FIG. 2 of U.S. Pat. No. 4,111,035 entitled "Engine knock signal generating apparatus with noise channel inhibiting feedback", for example.
In the engine knock control apparatus disclosed in this U.S. Pat. No. 4,111,035, the output from a knock sensor is applied to one of input terminals of a comparator through a bandpass filter to remove noise components while the output of the bandpass filter is first averaged by noise reference and is then applied to the other input terminal of the comparator so as to effect knock control by the output of the comparator.
However, the detection signal detected by the knock sensor generally involves amplitude fluctuation of as large as from .+-.5 (mV) to .+-.600 (mV) irrespective of the kind of the knock sensor. In order to correctly pick up and discriminate the knock signal, therefore, the signal must be leveled up to a discriminating level by use of an amplifier. If the detection signal is merely amplified by amplifiers in general, however, the detection signal can not be amplified up to a level that exceeds a battery voltage to be employed as a power source of the amplifier, because its maximum voltage is determined by the battery capacity.
If the gain of the amplifier is kept at a high level, the amplifier output would saturate when the knock signal is excessive, whereby an excessively large knock control signal is generated from the comparator and proper knock control becomes impossible. If the gain of the amplifier is kept at a low level, on the contrary, an excessively small knock control signal would be generated from the comparator when the knock signal is small, whereby proper knock control becomes impossible. For these reasons, the conventional engine knock control apparatus are not devoid of low reliability.